Up to now, the burning processes in the conversion of hydrocarbons, has always led only to an incomplete burning and conversion, whereby there resulted problems with carbon monoxide, unburned hydrocarbons, soot and other harmful materials, such as, for instance, nitric oxides. In order to avoid these difficulties, it has already been proposed to perform the burning in the bores of a ceramic, which is coated with a catalyst. In order to prolong the working life of the catalyst, it has to be coated on a porous ceramic carrier, so that on the other side, by means of correspondingly large surfaces, a complete conversion of the mixture flowing through it, is accomplished. This is preferably done in perforated stone plates or a honeycombed ceramic, however, also on ceramic substances shaped, for instance, like pellets, cylinders and filaments.
In order to perform this task, recently mainly substances containing platinum have been applied as catalysts which have the disadvantage, however, that platinum quickly becomes "poisoned" and therefore is ineffective due to impurities of the hydrocarbons to be burned, especially, for instance, soot and SO.sub.2, in the case of afterburning of motor vehicle exhaust gases.
Difficulties also arise with the utilization of a catalyst which has become known from the German Pat. No. 22 10 365, wherein a mixture of cobalt, lanthanum, nickel and uranium is provided as an active metal coating on a porous ceramic carrier, whereby the components, however, are finally always present as oxides. For the purpose of simplification, in the following, reference will be made only to the active metal components (which are contained in the oxides). Extensive tests, upon which the present invention is based, have proven that the therein proposed substances cannot be continuously utilized as a catalyst, because the nickel portion, as well as the uranium, in the long term causes the destruction of the catalyst because of a reaction with the ceramic carrier and its break-down, especially because of multispinel formation. The indicated extensive mixing ratio ranges of cobalt and lanthanum, to a large extent, do not result in a suitable catalyst, because if the ratio between a lanthanum nitrate portion and a cobalt nitrate portion is decreased during the impregnation of the carrier substance, the excess cobalt oxide very quickly escapes during workup of the catalyst and poisoning occurs. This "poisoning" of the catalyst results especially at higher temperatures, not only in the case of the above mentioned cobalt-lanthanum-nickel-uranium mixture, but also in the case of substances containing platinum, so that such catalysts, for instance, for the afterburning of combustion gases or exhaust gases of motor vehicles, have to be positioned in the cooler sections, far behind the burning device or engine. This has the disadvantage, however, that the conversion cannot be as complete as it would be at higher temperatures.
The object of the invention is to provide a catalyst for the conversion of hydrocarbons, which is stable and thoroughly insensitive to poisoning not only by harmful foreign materials, but also to self-poisoning at higher temperatures, and which also makes possible the reduction or conversion of harmful nitric oxides.